Perforating apparatus



Aug. 7, 1962 M. P. LEBOURG 3,048,102

PERFORATING APPARATUS Filed Jan. 30, 1959 MOO/V66 F? lebour INVENTOR.

ATTORNEY The present invention relates to perforating apparatus,

and, more particularly, to shaped charge perforating apparatus which isretrievable after firing through a string of tubing in a well and whichleaves little or no debris in the well. I So-called expendable type,shaped charge perforating apparatus has been developed which will passthrough tubing and is adapted to disintegrate upon detonation of thecharges thus leaving an amount of debris in the well. In one arrangementof this type, the shaped charges are disposed in individual,fluid-tight, thin-walled containers (commonly cal-led capsule charges)suitably linked to one another to form a chain of charges. Anotherarrangement has shaped charges disposed within a fluidtight, frangible,thin-walled housing. While these arrangements enjoy a certain degree ofsuccess, there is always a certain amount of debris from the containersor housmg which must be left in the well. Ordinarily, the debris is oflittle consequence, but in some applications it is desirable to reducethe debris left in the well.

One proposed solution to reduce the amount of debris left in the wellhas been to eliminate the linkages or frangible housing by placingcapsule charges in a retrievable frame or carrier member. However, thereduction of debris has not been significant since most of the debrisresults from the break-up of the capsule container itself. Additionally,after the carrier member has been exposed to one or more operations, itis distorted beyond use by the explosive pressures generated when thecharges are detonated. Therefore it will be appreciated that there is aneed for an inexpensive perforating apparatus which will reduce theamount of debris left in the well.

It is, accordingly, an object of the present invention to provide a newand improved shaped charge perforating apparatus for use in wells havinga string of tubing arranged so that the debris from detonated shapedcharges may be retrieved through the string of tubing.

It is a further object of the present invention to provide a new andimproved housing for shaped charge perforating apparatus for use inwells having a string of tubing wherein the housing and shaped chargestherein are so arranged that the explosive pressures generated upondetonation of the shaped charges do not unduly distort the housingthereby permitting the housing to be retrieved through the tubing.

Another object of the present invention is to provide new and improvedhousing for shaped charge perforating apparatus for use in wells havinga string of tubing wherein the housing is provided with a wall portionof reduced thickness adjacent a shaped charge to improve the performanceof the charge and control the outward protrusion of the burr caused byan explosive jet penetrating the wall portion upon detonation of ashaped charge.

A still further object of the present invention is to provide a new andimproved housing, for shaped charge perforating apparatus for use inwells having a string of tubing wherein the housing is both retn'evableand expendable and of simple and economic construction.

These and other objects of the present invention are accomplished byperforating apparatus having explosive shaped charges disposed within anelongated thin-Walled tubular housing which is adapted to retain thedebris upon detonation of the charges. The outer wall surface of thehousing is provided with a concavity or indentation adjacent to theforward end of a shaped charge so as 3,048,102 ?atented Aug. 7, 1962 tobe penetrated readily by the perforating jet of the charge and minimizethe outward protrusion of the burr caused by the jet thereby permittingthe housing to be retrieved through thestring of tubing.

The novel features of the present invention are set forth withparticularity in the appended claims. The present invention, both as toits organization and manner of operation together with further objectsand advantages thereof may best be understood by way of illustration andexample of certain embodiments when taken in conjunction with theaccompanying drawings in which:

FIG. 1 is an elevatioual view of perforating apparatus which embodiesthe present invention disposed below the lower end of a tubing string ina section of a cased borehole;

FIG. 2 is a view in longitudinal cross section illustrating a portion ofthe perforating apparatus shown in FIG. 1 before detonation of theshaped charge;

FIG. 3 is a transverse cross-sectional View taken along lines 33 of FIG.2;

And FIG. 4 is a longitudinal cross-sectional view of the portion of thehousing shown in FIG. 2 after detonation of the shaped charge.

Referring now to FIG. 1, a portion of a cased borehole 10 is showntraversing earth formations 11 and 12, the formation 12 being assumed tobe the formation of interest. A tubing string 14 extends downwardly fromthe ground surface to some point above the formation 12 while theannulus between the lower end of the tubing string 14 and the casedborehole 10 is suitably packed off by conventional packing means 15.Perforating apparatus 16 embodying the present invention is shown inposition adjacent earth formation 12 and generally includes a cable head17, a conventional casing collar locator 18, a tubular housing 19 and abottom nose piece 20 which fully closes the bottom end of the housing.Collar locator 18 and bottom nose piece 20 are coupled to the housing 19by suitable fluid-tight connections so that the housing is sealed withrespect to well fluids, although its interior remains at someappropriate pressure, as, for example, atmospheric pressure. Housing 19may be constructed of steel or any appropriate material having asufficient strength to resist well pressures and tc avoid disintegrationor undue distortion when the perforating apparatus is operated.

Apparatus 16 is adapted to be lowered through the borehole into aposition adjacent earth formation 12 and retrieved therefrom throughtubing 14 by means of a winch (not shown) at the ground surface and anarmored electrical cable 21 connected between the winch and the cablehead 17. While it is not shown, it is apparent that various means may beemployed to position the apparatus centrally in the borehole, forexample, conventional centralizing means. Likewise, eccentering means,sucl as the magnetic orienting device disclosed in the copendingapplication Serial No. 719,255, filed March 5, 1958 by Maurice P.Lebourg may be employed to eccentricall position the apparatus.

Spaced vertically from one another within housing 1! are a plurality ofconventional shaped charge explosive: 22 which are interconnected fordetonation by an igniting means 23 as, for example, a conventionalprimacord A detonator or blasting cap 24 for the primacord is con nectedthrough the electrical cable 21 to a control switcl (not shown) at thesurface so that the firing of th charges 22 may be initiatedelectrically in a well-know] manner.

As shown in detail in FIG. 2, housing 19 is a thin walled tubing memberwhich receives an elongated shapet charge 22 having a longitudinal axis28 which is dis posed transversely to the longitudinal axis 28a of thhousing. While only a portion of the housing and on shaped charge isshown, it should be understood tha other portions of the housing andcharges are similarly arranged, the charges being distributed along thehousing so as to face one of several directions in a customary fashion.

Shaped charge 22 includes an elongated hollow container 25 having aforward, tubular portion 26 and a rearward, frustoconical, thin-walledportion 27 which tapers inwardly from the tubular portion 26 towardslongitudinal axis 28 of the charge 22. The forward extremity 29 of thetubular portion 26 (FIG. 3) is suitably curved so as to conform to thecurvature of the inner wall 33 of the housing. At the rearward extremityof the container 25 is a semi-cylindrical recess 30 extendingtransversely to the longitudinal axis 28 of the charge which receivesthe primacord 23. With the primacord 23 in recess 30 the assembledprimacord and container may be slidably positioned within the housing19.

Container 25 is firmly secured and located within the housing by meansof a fixture 31 provided with an annular collar 32a which receives andis suitably fixed, as for example, by welding, to the forward tubularportion 26. An extension 3211 projects from the lower extremity ofcollar toward a wall portion of housing 19 adjacent to and below theforward extremity 29 of tubular portion 26 and joins a downwardlyextending tang 320 which conforms to and is in contact with the innerwall 33 of the housing. A threaded bore 34 in the lower end of the tang320 is adapted to be aligned with a lateral opening 35 in the wall ofthe housing so that a fastener 36, for example, a screw, may secure thecontainer 25 in a fixed position Within the housing with extremity 29engaging surface 33. It will be appreciated that so long as fastener 36engages threaded bore 34, the charge 22 is accurately positioned andfixed within the housing at all times.

The hollow container 25 is substantially filled with a high explosive 37and a small, conventional booster explosive material 38 is disposedadjacent to the primacord 23 at the rearmost end of the primaryexplosive 37. The explosive materials are composed of suitable materialswell known to those skilled in the art, for example, the boosterexplosive may be 98% cyclonite and 2% wax and the primary explosive,pure cyclonite. For a given size of container 25, the amount of primaryexplosive 37 may be decreased by the provision of an open-end,comically-shaped liner 40 or spacer fitted within the rearward portion27 of the container. It will, of course, be apparent that the size andshape of the liner 40, or of the container 25, may be varied toaccommodate any desired amount of explosive. The forward end of theprimary explosive material 37 is provided with a conicallyshaped cavityand fitted with a metal liner 41, for example, of copper, in awell-known manner.

In accordance with the present invention, a portion of the housing 19adjacent to the forward end of the lined cavity is cut away as best seenin FIG. 2 to form an indentation or concavity 42 disposed directly inthe path of the perforating jet which, of course, is generated upon thedetonation of the shaped charge. More specifically, the indentation 42is defined by an arc of an imaginary cylinder with the axis 44 of thecylinder transverse to the longitudinal axis 28 of the shaped charge andwith the axes 28, 44 lying in a common plane. The precise form of theindentation may be varied so long as the portion of the indentationwhich is to be penetrated is spaced between the inner and outer walls ofthe housing a sufficient distance. Moreover, the shape and size of theindentation and the thickness of the housing wall in the indentedportion should be arranged to resist deformation due to Well pressuresto be encountered. With proper spacing, the indentation, when penetratedby the explosive jet of the charge, contains the major portion of theburr within the cylindrical confines of the outer wall of the housing.

In operation, the perforating apparatus 16 is lowered through the tubing14 until it is disposed adjacent the formation to be penetrated.Thereafter the charges 22 are detonated in a well-known manner. Thedetonation of each of the charges 22 produces a perforating jet whichpierces a central portion of the indentation 42. A burr 45 (FIG. 4) isformed about the penetration hole '46 which extends outwardly from theperiphery of the hole and has a major portion remaining within theconfines of the cylinder defined by outer wall 43 of the housing. Smalltips of the burr 45 which may extend beyond the outer wall of thehousing are easily broken 01f upon contact with the tubing '14 or casingwhen the apparatus is raised. Fragments of the container 25 are retainedwith the housing 19 so that the debris may be retrieved with thehousing.

The explosive pressures generated by the detonated charges have a highorder of magnitude for a short period of time tending to expand theWalls of the housing particularly in a zone intersected by the planedefined by line 33 (FIG. 2) so that some bulging of the housing willoccur (FIG. 4). However, it will be appreciated that since the indentedportion of the housing adjacent the forward end of a shaped chargeretains the burr within the confines of the outer Wall of the housing,the bulging of the housing is the only factor remaining to hinderpassage of the housing through a small diameter tubing. It is, ofcourse, necessary to control the swelling of the housing so that thehousing is not split by the explosive forces.

The swelling of the housing may be controlled by adjusting the ratio ofthe explosive weight relative to the spacing of the shaped charge fromthe inner walls of the housing. For example, if the tubing 14 has anominal internal diameter of 2 /2 inches and the diameter of the housingis 2 inches then the swelling may be slightly less than a half-inch. Inactual practice, for a measure of safety the swelling is held to a lowvalue.

The following practical embodiments of the present invention serve toillustrate more clearly its applications, but are illustrative only andshould not be considered as limiting the scope of the invention in anysense.

Examples Housing CD. (in) 1% 1% 1% 2 2 s 2 2% Housing 1.1). (in)- 1% 1%1 1 ,4 1% 1 1% Material (U Wall Thickness (in.) A6 its V1 710 40 Weightof Explosive (gr. 4 4 8. 8 6 7. 0 7. 2 8. 8 Open Area A (sq. m.) 15 1515 15 15 15 15 Ratio of Weight of Explosive (grams) to Open Area (sq.in.) 26.7 26.7 58.6 33.3 46.7 48 58.6 Housing O.D. After Firing (lines33). 1 962 1 %2 296.2 2%; 2%2 2 2 ghotls per foot of Housing 2 4 2 4 2 22 we mg 34x2 2 9 2 External Fluid Pressure on Housing at A 362 M52 A2 A2time of firing p.s.i. (internal pressureatmosphnc) 500 500 2 1, 000 500500 600 500 1 Cold rolled mild steel.

1 Increased to prevent splitting of housing.

In the foregoing examples, the open area A is calculated by subtractingthe cross-sectional area of the container in the plane defined by lines33 from the area defined within the inner wall of the housing. It willbe noted that if the Weight of explosive for a given area A is increasedthe swelling will increase. Similarly, if the area is decreased for agiven weight of explosive the swelling increases. It has been found thatwhen the area A is decreased to a Zero value, the housing invariablysplits. Although the precise mathematical relationship between thevarious factors which control the swelling has not been found, the aboveexamples serve amply to illustrate the invention.

The indentation in the housing for the foregoing examples was an arc ofa cylinder having 2 /2 inches diameter with the thinnest portion of thewall measuring A of an inch. It has been found that with a minimumthickness of of an inch for the wall that the perforating apparatus canwithstand borehole pressures of at least 10,000 p.s.i.

It will be appreciated from the foregoing that the present inventionprovides a perforating apparatus adapted to be retrieved through tubingafter firing. This is accomplished by providing a wall portion ofreduced thickness adjacent the forward end of a shaped charge whichimproves the performance of the charge and controls the outwardprotrusion of the burr. The housing and shaped charge are also arrangedso that the bulging effect of the housing is controlled. It will befurther apparent that the debris from the charges is retained within thehousing. Since the housing may be made of ordinary stock material andlittle machining is required, the housing is simple and inexpensive tofabricate for perforating operations. Thus, although the housing isexpended upon one trip into a well, it is entirely within the economicsof perforating service.

While particular embodiments of the present invention have been shownand described, it is apparent that changes and modifications may be madeWithout departing from this invention in its broader aspects, andtherefore the aim in the appended claims is to cover all such changesand modifications as fall within the true spirit and scope of thisinvention.

What is claimed is:

1. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level desired to be perforated and adapted to retrieve the debrisfrom the shaped charges therein comprising: an elongated, functionallyintegral tubular housing including inner and outer cylindrical wallsurfaces, a portion of said housing having a bore of uniform diameterdefined by said inner wall surface and having at least one indentationtherein which extends inwardly from said outer wall surface towards saidinner wall surface thereby forming a wall portion of reduced thickness,said wall portion of reduced thickness having sufiicient strength toresist the effects of borehole pressures encountered, and being spacedinwardly from said outer wall surface a sufficient distance to containthe major portion of a burr formed within the cylindrical confines ofsaid outer wall surface when the Wall portion is penetrated, andperforating means disposed within said housing and sized to extendacross substantially the diameter of said bore, said perforating meansincluding an explosive material having a forward, hollowed-out endportion positioned adjacent to said wall portion of reduced thickness.

2. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level desired to be perforated and adapted to retrieve the debrisfrom the shaped charges therein comprising: an elongated, functionallyintegral tubular housing having a longitudinal axis and including innerand outer cylindrical wall surfaces, a portion of said housing having abore of uniform diameter defined by said inner wall surface and havingat least one concavity therein which extends inwardly from said outerwall surface towards said inner wall surface thereby forming a wallportion of reduced thickness, said wall portion of reduced thicknesshaving sufficient strength to resist the efiects of borehole pressuresencountered and being spaced inwardly from said outer wall surface asufficient distance to contain the major portion of a burr formed withinthe cylindrical confines of said outer wall surface when the wallportion is penetrated, and perforating means disposed within saidhousing and sized to extend across substantially the diameter of saidbore, said perforating means including an explosive material having aforward hollowedout end portion positioned adjacent to said wall portionof reduced thickness, the cross-sectional area of said perforating meanstransverse to said longitudinal axis being less than the cross-sectionalarea defined within said inner wall surface to provide an air spacethereby minimizing the bulging effect caused by detonation of saidexplosive.

3. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of tubing between the ground surface and a leveldesired to be perforated and adapted to retrieve the debris from theshaped charges therein comprising: an elongated, functionally integraltubular housing having a longitudinal axis and including inner and outercylindrical wall surfaces, a portion of said housing having a bore ofuniform diameter defined by said inner wall surface and having at leastone concavity extending inwardly from said outer Wall surface towardssaid inner wall surface thereby forming a wall portion of reducedthickness, said wall portion of reduced thickness having suificientstrength to resist the effects of borehole pressures encountered andbeing spaced inwardly from said outer wall surface a sufficient distanceto contain the major portion of a burr formed Within the cylindricalconfines of said outer wall surface when the wall portion is penetrated,and perforating means disposed within said housing and sized to extendacross substantially the diameter of said bore, said perforating meansincluding an explosive material having a forward, hollowed-out endportion positioned adjacent said wall portion of reduced thickness, thecross-sectional area of said perforating means transverse to saidlongitudinal axis being less than the cross-sectional area defined with.in said inner wall surface to provide an air space thereby minimizingthe bulging effect caused by detonation of said explosive, saidconcavity having an outer periphery on said outer surface which isgreater than the periphery of a hole through said wall portion ofreduced thickness caused by detonation of said explosive material.

4. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level desired to be perforated and adapted to retrieve the debrisfrom the shaped charges therein comprising: anelongated, functionallyintegral tubular housing constructed of ductile material throughout itslength and having a relatively thin wall, said housing further having alongitudinal axis and having inner and outer cylindrical wall surfaces,a portion of said housing having a bore of uniform diameter defined bysaid inner wall surface and having at least one indentation in the outersurface thereby forming a wall portion of reduced thickness, perforatingmeans disposed within said housing and sized to extend acrosssubstantially the diameter of said bore, said perforating meansincluding an explosive material having a forward hollowed-out endportion positioned adjacent said wall portion of reduced thickness, saidindentation being spaced between said inner and outer surfaces so thatupon penetration by an explosive jet, the major portior of a burr formedwill lie within the cylindrical confines of said outer surface.

5. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level to be perforated and adapted to retrieve the debris from theshaped charges therein comprising: an elongated, functionally integraltubular housing having a longitudinal axis and including inner and outercylindrical wall surfaces, a portion of said housing having a bore ofuniform diameter defined by said inner wall surface and having at leastone indentation in the outer surface thereby forming a wall portion ofreduced thickness, said indentation being defined by the arc of animaginary cylinder having an axis transversely positioned relative tosaid longitudinal axis, perforating means disposed within said housingand sized to extend across substantially the diameter of said bore, saidperforating means including an explosive material having a forwardhollowed-out end portion positioned adjacent said wall portion ofreduced thickness, said indentation being spaced between said inner andouter surfaces so that upon penetration by an explosive jet, the majorportion of a burr formed will lie within the cylindrical confines ofsaid outer surface.

6. A Shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level to be perforated and adapted to retrieve the debris from theshaped charges therein comprising: an elongated, functionally integraltubular housing having a longitudinal axis and including inner and outercylindrical Wall surfaces, a portion of said housing having a bore ofuniform diameter defined by said inner wall surface and having at leastone indentation in the outer surface thereby forming a wall portion ofreduced thickness, said indentation being defined by the arc of animaginary cylinder having an axis transversely positioned relative tosaid longitudinal axis, said housing further having at least onelocation opening for each indentation spaced longitudinally from anindentation, perforating means sized to be slidably received through oneof the ends of said housing and extend across substantially the diameterof said bore, said perforating means including a hollow container havinga preselected fastening location disposed longitudinally from saidhollow container a distance comparable to the longitudinal spacingbetween said location opening and said indentation, an xplosive materialhaving a forward hollowed-out end portion in said container positionedadjacent said wall portion of reduced thickness, said for- Ward endportion thereby being disposed in a preselected position relative tosaid fastening location, said indentation being spaced between saidinner and outer surfaces so that upon penetration by an explosive jet,the major portion of a burr formed will lie within the cylindricalconfines of said outer surface, and fastening means adapted to extendthrough said location opening into said preselected fastening locationto secure said container to said housing and thereby provide anindication of the location of the forward end portion of said explosivematerial.

7. A shaped charge perforating apparatus sized to be lowered and raisedthrough a string of small-diametered tubing between the ground surfaceand a level to be perforated and adapted to retrieve the debris from theshaped charges therein comprising: an elongated, functionally integraltubular housing having a longitudinal axis and including inner and outercylindrical wall surfaces, a portion of said housing having a bore ofuniform diameter defined by said inner wall surface and having at leastone indentation in the outer surface thereby forming a wall portion ofreduced thickness, said indentation being defined by the arc of animaginary cylinder having an axis transversely positioned relative tosaid longitudinal axis, said housing further having at least onelocation opening for each indentation spaced longitudinally from anindentation, perforating means sized to lie disposed within said housingthrough one of the ends of said housing, said perforating meansextending across substantially the diameter of said bore and including ahollow container having a portion with a threaded bore, an explosivematerial having a forward hollowed-out end portion in said containerpositioned adjacent said wall portion of reduced thickness, said forwardend portion thereby being disposed in a preselected position relative tosaid threaded bore, said indentation being spaced between said inner andouter surfaces so that upon penetration by an explosive jet the majorportion of a burr formed will lie within the cylindrical confines ofsaid outer surface, and screw means adapted to extend through saidlocation opening into said threaded bore to secure said container tosaid housing and thereby provide an indication of the location of theforward end portion of said explosive material.

8. A shaped charge perforating apparatus comprised of: an elongated,functionally integral tubular housing having selected areas along itslength, said housing having location openings respectively displacedfrom said selected areas of the housing so as to avoid coincidencetherewith, a plurality of hollow containers sized to be disposed withinsaid housing through one of the ends of said housing and sized to extendacross substantially the diameter in said housing, said containersrespectively having a preselected fastening portion displaced from thehollow portion of said containers so that when said fastening portionsare aligned with said location openings the hollow portions are adjacentsaid selected areas; explosive material having a forward hollowed outend portion for developing a perforating jet disposed in the hollowportion of each of said containers so that said explosive material whendetonated will develop a perforating jet through a selected area; andfastening means arranged to extend through said location openings forsecuring said fastening portions to said housing to insure alignment ofthe perforation jets with said selected areas and to provide anindication of such alignment.

9. A shaped charge perforating apparatus comprised of: an elongated,functionally integral tubular housing member having selected areas alongits length, said housing having location openings respectively displacedfrom said selected areas of the housing so as to avoid coincidencetherewith, a plurality of hollow containers sized to be disposed withinsaid housing through one of the ends of the said housing and sized toextend across substantially the diameter in said housing, saidcontainers respectively having a threaded bore portion displaced fromthe hollow portion of said containers so that when said threaded boreportions are aligned with said location openings the hollow portions areadjacent said selected areas; explosive material having a forwardhollowed out end portion for developing a perforating jet disposed inthe hollow portion of each of said containers so that said explosivematerial when detonated will develop a perforating jet through aselected area; and screw means arranged to extend through said locationopenings for securing said threaded bore portions to said housing toinsure alignment of the perforating jets with said selected areas and toprovide an indication of such alignment.

10. Perforating apparatus comprising: a thin-walled, tubular, ductile,metallic, functionally integral housing sized for passage through asmall-diametered well string with minimum safe clearance, said housingin its normal condition having cylindrical inner and outer surfaces freeof protuberances, said housing having a series of cylindrically curvedconcavities spaced longitudinally of said housing along its outersurface, the axes of said housing and said concavities being transverse,a plurality of shaped charges sized for slidable positioning within saidhousing in a transverse position with their front end conforming to saidinner surface, means extending longitudinally of said shaped chargeswithin said housing for positioning said charges having front endportions aligned with respect to each of said concavities, and means forclosing the ends of said housing against entry of fluid and escape ofdebris, the front end of each shaped charge being substantiallyco-extensive with the corresponding concavity to form a perforation burrcentrally of such concavity substantially Within the cylindrical profileof said outer surface.

11. Perforating apparatus comprising: a thin Walled, tubular, ductile,metallic, functionally integral housing having cylindrical inner andouter surf-aces, said housing having a bore of uniform diameter definedby said inner wall surface and having a series of cylindrically curvedconcavities in said outer surface which are spaced longitudinally fromone another, a plurality of shaped charges positioned Within saidhousing arranged to produce perforating jets along perforating axestransverse to the axis of said housing, said shaped charges extendingacross substantially the diameter of said bore, means for se- 10 curingsaid shaped charges relative to said housing so that their front endportions respectively are centrally aligned with a concavity, so that aperforation burr formed \by a perforating jet penetrating a concavitylies substantially within the cylindrical profile of said outer surface.

References Cited in the file of this patent UNITED STATES PATENTS

